Process for preparing alumina carrier

ABSTRACT

PCT No. PCT/JP96/02870 Sec. 371 Date Jun. 2, 1997 Sec. 102(e) Date Jun. 2, 1997 PCT Filed Oct. 3, 1996 PCT Pub. No. WO97/12670 PCT Pub. Date Apr. 10, 1997An alumina catalyst carrier is prepared by using an alumina material comprising 90 to 20% by weight of alumina as particles having an aspect ratio of 1 to 5, and 10 to 80% by weight of alumina as particles having an aspect ratio of more than 10 but less than 10,000; kneading and forming the alumina material, and then calcining the formed product. The resulting catalyst carrier has high strength, and has such a pore diameter distribution as to give satisfactory catalytic activity.

TECHNICAL FIELD

This invention relates to a process for preparing an alumina carrier foruse as a carrier for various catalysts. More specifically, the inventionrelates to a process for preparing a high-strength, high-activityalumina catalyst carrier from alumina having an aspect ratio of 1 to 5and alumina having an aspect ratio of more than 10 but less than 10,000.

BACKGROUND ART

Preparation of an alumina catalyst carrier from alumina generally uses astep of kneading an alumina material, a step of forming the kneadedmaterial into a desired shape (such as cylinder, pellet or honeycomb)and a desired size, a step of drying the formed product at a temperatureof 80 to 150° C., and a step of calcining the dried product in acalciner at a calcination temperature of 400 to 1,000° C.

Such an alumina catalyst carrier is required to have high activity andhigh strength. It is difficult to fulfill both of these requirements,and attempts have been made to do so. Japanese Laid-Open PatentPublication No. 8445/91 of the applicant, for example, discloses aprocess for preparing an alumina carrier which comprises adding an acidto a slurry consisting of an alumina hydrate and water to make pH2.0-3.0, then adding an alkali to adjust the pH of the slurry to3.5-6.0, and then separating an alumina hydrogel prior to the kneadingof a starting alumina powder. The use of this method makes it possibleto adjust the pore diameters of an alumina carrier, thereby improvingthe activity of a catalyst.

Japanese Laid-Open Patent Publication No. 235737/92 discloses a methodcomprising pressure molding water-containing alumina, followed by anaging and calcining process. This method is described as being capableof obtaining an alumina carrier having pores of 1,000 angstroms or morein diameter and having high mechanical strength. This publication,moreover, discloses a method which involves impregnating the aluminacarrier with an aqueous solution of an aluminum salt, followed by adrying and calcining process, to further enhance its mechanicalstrength.

Japanese Laid-Open Patent Publication No. 98486/75 discloses a processfor preparing a high-strength, high-activity alumina catalyst carrier byadding an acidic substance, such as acetic acid, and water to alumina,kneading them, forming the mixture, and calcining the formed product.

Japanese Laid-Open Patent Publication No. 27436/92 discloses ahydrogenation catalyst using an alumina catalyst in which the lengths ofalumina particles after forming and calcination steps have apredetermined distribution. This publication also discloses a processfor preparing the hydrogenation catalyst. This process is described asbeing excellent in desulfurization activity.

Japanese Laid-Open Patent Publication No. 205990/94 discloses theproduction of a high-activity catalyst for the hydrogenation anddesulfurization of a metal-containing heavy oil by use of an aluminacarrier having a specific pore diameter distribution. In Example A ofthis publication, an alumina material comprising two kinds of aluminaparticles, Catapal alumina and Versal 250 alumina is used for thepreparation of a catalyst carrier. No mention is made, however, of theaspect ratios of these alumina particles.

An alumina catalyst carrier is required to have pore diameters of aboutseveral tens of nanometers and a narrow pore diameter distribution inorder to achieve improved catalytic activity. To produce a catalystcarrier having such characteristics, it is desirable to use the startingalumina particles with an aspect ratio of 5 or less. The catalystcarrier, however, should also have a large specific surface area andpore volume to have high catalytic activity, thus making it impossibleto proceed fully with the sintering of the particles. Thus, whenparticles with an aspect ratio of 1 to 5 are used as an aluminamaterial, such particles can be joined to each other only at the site ofcontact between the particles at the time of calcination. The resultingcatalyst carrier is so low in mechanical strength as to undergo chippingor dusting.

When fibrous particles having an aspect ratio of greater than 10 areused as the starting material, on the other hand, the fibrous particlesare entangled during kneading, thus increasing the strength of theresulting catalyst carrier. This effect increases as the aspect ratiobecomes higher. The carrier using such a starting material is low incatalytic activity because of a broad pore diameter distribution.

The object of the present invention is to provide a process forpreparing an alumina catalyst carrier having sufficient mechanicalstrength, being capable of imparting high catalytic activity, andminimally undergoing chipping or dusting.

DISCLOSURE OF INVENTION

To attain this object, the inventors have focused on alumina materials,and conducted extensive studies. As a result, they have succeeded ineasily producing an alumina catalyst carrier with a desired range ofpore diameter distribution and improved mechanical strength by using analumina material containing alumina and fibrous alumina in predeterminedproportions, the alumina being particles having an aspect ratio of 1 to5, and the fibrous alumina being particles having an aspect ratio ofgreater than 10.

The present invention provides a process for preparing an aluminacarrier by kneading and forming an alumina material, and then calciningthe formed product, characterized in that;

the alumina material is composed of 90 to 20% by weight of alumina beingparticles having an aspect ratio of 1 to 5, and 10 to 80% by weight ofalumina being particles having an aspect ratio of more than 10 but lessthan 10,000.

The alumina material used in the process of the present invention iscomposed of 90 to 20% by weight of alumina being particles having anaspect ratio of 1 to 5, and 10 to 80% by weight of alumina beingparticles having an aspect ratio of more than 10 but less than 10,000.In this specification, the proportions (% by weight) of aluminas in thealumina material refer to their proportions to all aluminas in thematerial. If the proportion of the alumina being particles having anaspect ratio of more than 10 but less than 10,000 is less than 10% byweight, there will be no marked improvement in the strength of thealumina carrier after sintering. If the proportion of the alumina beingparticles having an aspect ratio of more than 10 but less than 10,000exceeds 80% by weight, the pore diameter distribution of the resultingalumina carrier will be broad, resulting in unsatisfactory catalyticactivity. To suppress the broadening of the pore diameter distributionof the alumina carrier, the aspect ratio of the particles of the aluminaused should be less than 10,000. To emphasize catalytic activity, it isdesirable to use alumina being particles having an aspect ratio of 1,000or less, preferably 200 or less, and more preferably 100 or less.

Under these circumstances, a more preferable composition of the aluminamaterial is 80 to 50% by weight of alumina being particles having anaspect ratio of 1 to 5, and 20 to 50% by weight of alumina beingparticles having an aspect ratio of more than 10 but less than 10,000;and more preferably 80 to 65% by weight of alumina being particleshaving an aspect ratio of 1 to 5, and 20 to 35% by weight of aluminabeing particles having an aspect ratio of more than 10 but less than1,000.

The term "particles of alumina" used herein refers to primary particlesof alumina, or secondary particles resulting when the primary particlesare agglomerated and oriented in a certain direction. Thus, theparticles whose agglomerate is easily dispersed into primary particlesrefer to primary particles of alumina; whereas the particles whoseagglomerate is not dispersed mean secondary particles of alumina.

The term "the aspect ratio" used herein is the ratio of the major-axislength to the minor-axis length of the particle. For example, the aspectratio can be determined by observing the particles with a transmissionelectron microscope or the like, randomly sampling 10 of the particlespresent in the image field, measuring the ratio of the major-axis lengthto the minor-axis length of each particle, and calculating the averageof the values. Thus, the lower limit of the aspect ratio is 1.

The alumina particles having an aspect ratio of 1 to 5, and aluminaparticles having an aspect ratio of more than 10 but less than 10,000that constitute the alumina material are commercially available.Alternatively, these aluminas with different aspect ratios can besynthesized under adjusted reaction conditions by a wet process, such ashydrolysis of an aluminum alkoxide, or neutralization between an acidicaluminum source, such as aluminum sulfate, aluminum nitrate or aluminumchloride, and a basic aluminum source, such as aluminum hydroxide orsodium aluminate. Preferred alumina is, although not restricted to,pseudo-boehmite type alumina, and alumina such as bialite or gibbsitemay be used.

The above commercially available or synthesized alumina particles havingan aspect ratio of 1 to 5, and alumina particles having an aspect ratioof more than 10 but less than 10,000, are mixed in the aforementionedproportions to give the alumina material. Alternatively, during thekneading of the alumina material, alumina having one of the aspect ratioranges may be added so as to form the aforesaid composition, whilealumina having the other aspect ratio range is being kneaded. Eachalumina may be in the form of a hydrate, a hydrous alumina cake of thehydrate, or an alumina slurry thereof.

Those two types of aluminas different in the aspect ratio range can bedirectly synthesized in the following manner: For the preparation of thealumina particles having an aspect ratio of 1 to 5, aluminum sulfate asan acidic aluminum source and sodium aluminate as a basic aluminumsource are neutralized and aged. Then, the precipitate is washed andfiltered. The alumina particles having an aspect ratio of more than 10but less than 10,000, on the other hand, can be prepared from an aluminahydrate that has been obtained by the neutralization of an acidicaluminum source with a basic aluminum source, or an acidic aluminumsource with a basic aqueous solution, or an acidic solution with a basicaluminum source. Examples of the acidic aluminum source are aluminumchloride, and chloride ion-containing aluminum sulfate. Examples of thebasic aluminum source include sodium aluminate.

The resulting cake may be subjected, as such, to kneading, or slurriedwith the addition of water and dried with a spray dryer to form apowder. The latter method is favorable because it facilitatescontrolling of the conditions used during kneading.

According to a preferred embodiment of the present invention, it ispreferred to use for the alumina material of the invention an aluminahydrate as primary particles having an aspect ratio of 1 to 5, or ahydrous alumina cake or an alumina slurry of the alumina hydrate; and ahydrous alumina cake or an alumina slurry which is prepared from analumina hydrate synthesized by the wet process and which has an aspectratio of 10 to 10,000 in the form of primary particles.

In accordance with the process for production of the alumina carrier ofthe invention, the alumina material prepared in the above manner iskneaded. Normally, an acid or an alkali is added as a deflocculant,whereafter water is added to impart a water content for formability,followed by kneading the mixture. An acidic solution or an alkalinesolution capable of deflocculating the alumina material is used for thispurpose. Examples of acids for the acidic solution are inorganic acidssuch as nitric acid, sulfuric acid and hydrochloric acid, and organicacids such as acetic acid, citric acid and oxalic acid. Nitric acid andorganic acids are particularly preferred since they leave no residuesduring a subsequent calcination step. Examples of alkalis for thealkaline solution are ammonia, quaternary ammonium hydroxides such astetrapropylammonium hydroxide, sodium hydroxide, potassium hydroxide,and sodium aluminate. Particularly preferred are ammonia and quaternaryammonium hydroxides, which leave no residues during the subsequentcalcination step.

The kneading step may be performed in the following manner with theaddition of an acid or an alkali within a specific pH range in place ofwater: An acidic or alkaline solution is added as a deflocculant to thealumina particles at the initial stage of kneading, followed by kneadingthe mixture while adding an acidic solution with a pH 3 or less or analkaline solution with a pH 11 or more. Research by the inventors showedthat kneading with the use of the solution within the above pH rangeincreased the strength of the calcined alumina carrier by about 25% toabout 60% over kneading with the use of water. For the use of the acidicsolution, pH 1 or less is particularly preferred. In the case of thealkaline solution, those with a pH of 13 or more are particularlypreferred. The solubility of alumina has been found the lowest with useof pH 5, and found to increase as the pH becomes more acidic or morealkaline than this value. The acid or alkali as an alternative to watermay be the aforementioned type of acidic or alkaline solution.

The kneaded alumina particles are generally formed into a suitable sizeand a suitable shape by a forming machine. Then, the formed product isdried, for example, for 10 minutes to a whole day at a temperature of 80to 150° C. by means of a dryer. Then, the dried product is calcined at atemperature of, say, 400 to 1,000° C. in a calciner.

BEST MODE FOR CARRYING OUT THE INVENTION

The process for preparing an alumina carrier of the present inventionwill now be described by way of Examples, but the invention is in no waylimited thereto.

Example 1

As alumina, there was used 1,800 g of commercially availablepseudo-boehmite formed from particles having an aspect ratio of 1 to 5(average 2.0), the boehmite being called alumina A. Alumina A was mixedwith 200 g of commercially available pseudo-boehmite formed fromparticles having an aspect ratio of 30 to 100 (average 58), the boehmitebeing called alumina B, to prepare an alumina material. The proportionof alumina B mixed was 10% by weight. At the initial stage of kneadingthe alumina material, 1 liter of 3.3% nitric acid was added as adeflocculant. Then, while kneading the mixture, water was added wherenecessary to adjust the water content of a final dough to 45 to 60% byweight. After kneading for 2 hours, the dough was formed into a columnarshape 1 mm in diameter by a twin-screw extruder. The formed product wasdried in a dryer for 20 hours at 130° C. Then, after drying the pelletswere calcined in a calciner for 1 hour at 600° C. to obtain an aluminacatalyst carrier.

The average flexural strength and side collapse strength (SCS) of thealumina catalyst carrier were measured with a universaltension/compression tester and a Toyama tablet strength measuringmachine, respectively. The average flexural strength was 10.2 MPa, andthe SCS was 1.9 kg. Measurement was also made of a value on which thelengths of the alumina carrier dropped several times from a height of 2m onto a stainless steel plate converged (convergent length). Theconvergent length expressed as the average of the alumina carrierlengths after the 5th and the 7th dropping was 2.1 mm. Preliminaryexperiments showed the convergent length of the alumina carrier becomeslarger in proportion to the increase in the flexural strength of thealumina carrier. The results are shown in Table 1. In Table 1, themixing ratio (% by weight) is the proportion (% by weight) of thealumina particles having an aspect ratio of 1 to 5 to all aluminascontained in the starting powdery material.

                  TABLE 1    ______________________________________           Mixing ratio of           alumina particles                      Flexural        Convergent           having aspect ratio                      strength SCS    length           of 1 to 5 (wt. %)                      (MPa)    (kg)   (mm)    ______________________________________    Ex. 1    90           10.2     2.2  2.3    Ex. 2    70           11.8     2.6  2.5    Ex. 3    50           15.5     3.0  2.8    Ex. 4    20           20.0     3.3  3.1    Ex. 5    80           14.3     3.1  2.9    Comp. Ex. 1             100          8.6      1.9  2.1    Comp. Ex. 2             0            21.5     3.5  3.2    ______________________________________

Example 2

The alumina material was kneaded, formed, dried and calcined in the sameway as in Example 1, except that the proportion of alumina B mixed was30% by weight. The resulting alumina carrier was measured for theaverage flexural strength, SCS and convergent length in the same manneras in Example 1. The results are shown in Table 1.

Example 3

The alumina material was kneaded, formed, dried and calcined in the sameway as in Example 1, except that the proportion of alumina B in thealumina material was 50% by weight. The resulting alumina carrier wasmeasured for the average flexural strength, SCS and convergent length inthe same manner as in Example 1. The results are given in Table 1.

Example 4

The alumina material was kneaded, formed, dried and calcined in the sameway as in Example 1, except that the proportion of alumina B in thealumina material was 80% by weight. The resulting alumina carrier wasmeasured for the average flexural strength, SCS and convergent length inthe same manner as in Example 1. The results are presented in Table 1.

Example 5

There were prepared 12 liters of a 0.25M aqueous solution of aluminumsulfate as an acidic aluminum source, and 9.5 liters of a 0.5M aqueoussolution of sodium aluminate as a basic aluminum source. After 20 litersof water were added to the aqueous aluminum sulfate solution, theaqueous sodium aluminate solution was added at 25° C. to carry out theneutralization reaction. The reaction was controlled so that the pH whenneutralization took place would be 7.0±0.2. After the reaction, thetemperature of the reaction mixture was held at 80° C., followed byadding an aqueous solution of sodium hydroxide to adjust the pH to 10.The mixture was aged for 20 hours with stirring. Then, the aged mixturewas washed and filtered to obtain an alumina cake in which the particleshad an aspect ratio of 1 to 5 (average 2.3), the alumina cake beingcalled alumina C.

Then, 12 liters of a 0.5M aqueous solution of aluminum chloride as anacidic aluminum source, and 9.5 liters of a 0.5M aqueous solution ofsodium aluminate as a basic aluminum source were prepared. After 20liters of water were added to the aqueous aluminum chloride solution,the aqueous sodium aluminate solution was added at 70° C. to carry outthe neutralization reaction. The reaction was controlled so that the pHwhen neutralization took place would be 8.3±0.2. After the reaction, thetemperature of the reaction mixture was held at 80° C., followed byadding an aqueous solution of sodium hydroxide to adjust the pH to 9.The mixture was aged for 20 hours with stirring. Then, the aged mixturewas washed and filtered to obtain an alumina cake in which the particleshad an aspect ratio of 30 to 80 (average 48), the alumina cake beingcalled alumina D.

Water was added to the alumina C cake (80% by weight as a dry powder)and the alumina D cake (20% by weight as a dry powder), followed bymixing, to form an alumina slurry. Then, the alumina slurry was driedwith a spray dryer to obtain an alumina powder containing two kinds ofaluminas with different aspect ratio ranges in the above proportions.The obtained alumina powder was used as the starting powdery materialinstead of the staring powdery material used in Example 1. The aluminapowder was kneaded, formed, dried and calcined in the same way as inExample 1. The resulting alumina carrier was measured for the averageflexural strength, SCS and convergent length in the same manner as inExample 1. The results are given in Table 1.

Comparative Example 1

The alumina material was kneaded, formed, dried and calcined in the sameway as in Example 1, except that only alumina A was used, and alumina Bwas not mixed. The resulting alumina carrier produced only from aluminaA was measured for the average flexural strength, SCS and convergentlength in the same manner as in Example 1. The results are given inTable 1.

Comparative Example 2

The alumina material was kneaded, formed, dried and calcined in the sameway as in Example 1, except that only alumina B was used as the aluminamaterial. The resulting alumina carrier was measured for the averageflexural strength, SCS and convergent length in the same manner as inExample 1. The results are shown in Table 1.

In the Examples 1 to 5 and Comparative Examples 1 and 2, the totalweight of the alumina material was identical.

Determination of Pore Diameter Distribution

The pore diameter distributions of the alumina catalyst carriersobtained in the Examples 1 to 5 and Comparative Examples 1 and 2 wereinvestigated using ASAP2400 (Micromellitex). Table 2 shows the rates ofthe pore volumes within specific pore diameter ranges to the total porevolume. The higher their values are, the more concentrated the pores arein specific ranges. This means a sharper pore diameter distribution andbetter catalytic activity. In Table 2, the pore diameters of thecatalyst carriers obtained when the mixing ratio of alumina B was up to80% by weight were distributed in narrow ranges of from 80 to 120angstroms. When the alumina material was composed entirely of alumina B(Comp. Ex. 2), by contrast, the pore diameter distribution was broad.Example 5, using alumina D with a lower aspect ratio compared to aluminaB, tended to give a sharp pore diameter distribution and sufficientstrength.

                  TABLE 2    ______________________________________    Mixing ratio of    alumina particles Pore volume rate (%)    having aspect ratio                      Pore diameter                                 Pore diameter    of 1 to 5 (wt. %) 90-110 A   80-120 A    ______________________________________    Ex. 1   90            52         70    Ex. 2   70            46         64    Ex. 3   50            41         61    Ex. 4   20            31         54    Ex. 5   80            51         69    Comp. Ex. 1            100           54         72    Comp. Ex. 2            0             23         45    ______________________________________

Industrial Availability

As described above, an alumina carrier obtained in the present inventionby using an alumina material comprising 90 to 20% by weight of aluminabeing particles having an aspect ratio of 1 to 5, and 10 to 80% byweight of alumina being particles having an aspect ratio of greater than10 but less than 10,000 has improved mechanical strength, and sufficientpore diameter distribution to impart satisfactory catalytic activity.The use of alumina prepared in Example 5 fulfills both of desiredcarrier strength and desired pore diameter distribution. Thus, theprocess for preparing the alumina carrier of the present invention isvery effective for producing a catalyst having high strength andsatisfactory catalytic activity.

I claim:
 1. A process for preparing an alumina carrier by kneading andforming an alumina material, and then calcining the formed productcharacterized in that;said alumina material is composed of 90 to 20% byweight of pseudo-boehmite particles having an aspect ratio of 1 to 5,and 10 to 80% by weight of pseudo-boehmite particles having an aspectratio of more than 10 but less than 10,000.
 2. The process of claim 1,wherein said pseudo-boehmite particles having the aspect ratio of 1 to 5are added to said pseudo-boehmite particles having the aspect ratio ofmore than 10 but less than 10,000 while said pseudo-boehmite particleshaving the aspect ratio of more than 10 but less than 10,000 are beingkneaded.
 3. The process of claim 1, wherein said alumina material isprepared by mixing said pseudo-boemite particles having the aspect ratioof 1 to 5 and said pseudo-boemite particles having the aspect ratio ofmore than 10 but less than 10,000.
 4. The process of claim 1, whereinsaid alumina material is prepared by using a hydrous alumina cake orslurry of said pseudo-boehmite particles having the aspect ratio of 1 to5 and a hydrous alumina cake or slurry of said pseudo-boehmite particleshaving the aspect ratio of more than 10 but less than 10,000.
 5. Theprocess of claim 4, wherein said hydrous alumina cake or slurry of saidpseudo-boehmite particles having the aspect ratio of more than 10 butless than 10,000 has been prepared from an alumina hydrate obtained bythe neutralization reaction between an acidic aluminum source and abasic aluminum source, or an acidic aluminum source and a basic aqueoussolution, or an acidic aqueous solution and a basic aluminum source. 6.The process of claim 4, wherein said pseudo-boehmite particles havingthe aspect ratio of 1 to 5 and said pseudo-boehmite particles having theaspect ratio of more than 10 but less than 10,000 are each obtainedthrough a wet process.
 7. The process of claim 1, wherein saidpseudo-boehmite particles having the aspect ratio of more than 10 butless than 10,000 are added to said pseudo-boehmite particles having theaspect ratio of 1 to 5 while said pseudo-boehmite particles having theaspect ratio of 1 to 5 are being kneaded.
 8. A process for preparing analumina carrier by kneading and forming an alumina material, and thencalcining the formed product characterized in that;said alumina materialis composed of 90 to 20% by weight of pseudo-boehmite particles havingan aspect ratio of 1 to 5, and 10 to 80% by weight of pseudo-boehmiteparticles having an aspect ratio of more than 10 but less than
 200. 9.The process of claim 8, wherein said alumina material is composed of 80to 50% by weight of said pseudo-boehmite particles having the aspectratio of 1 to 5, and 20 to 50% by weight of said pseudo-boehmiteparticles having the aspect ratio of more than 10 but less than 200.